Duplicated Unique items

I've been completing the Monk Quests. I had Monk from 1.0, so when you have the lvl 45 Monk Quest you receive 4 pieces of the AF. At this point, i had the full AF already, so when i opened a box, i received a second pair of "Temple Gaskings". I didn't get the other pieces because i had them in my inventory already, but i got a second pair of "Temple Gaskings" because my original piece was in one of my retainers...

It's kinda annoying because you can't discard or sell this duplicate

Right now i'm doing BLM quests. It's happening again